Nucleic acid selection, i.e., in vitro selection has proven to be an extremely versatile technique for the isolation of aptamers that can bind tightly and specifically to target molecules. Aptamers, i.e., selected nucleic acid-binding species, have begun to be developed for therapeutic applications and as research reagents. Moreover, because nucleic acid selection can quickly yield compounds that have unique properties and that can be applied in unique roles, this technique offers much potential as a tool to augment drug discovery efforts. In many ways, the generation of a particular aptamer resembles evolution in that it starts from a random mixture of oligonucleotides and then selects for the 'best' sequences in a process called 'systematic evolution of ligands by exponential enrichment' (SELEX). Aptamer diversity is generated via chemically synthesized random pools comprised of 30 to 200 nucleotide long randomized residues with rare and unique functional properties 10,000 to 100,000,000 times greater variation than that of the human immune system. However, in vitro selection (SELEX) of nucleic acid species (aptamers) is a repetitive time-consuming process; one that in general is poorly adapted to high-throughput applications. Microfabricated analytical devices offer significant potential advantages over standard laboratory instrumentation such as speed, cost, sample/reagent consumption, contamination, efficiency, and automation. Using a microfluidic silicon chip, preliminary data presented here indicate 'compatibility' of the in vitro selection (SELEX) component reactions (Chambers, et al.) required for aptamer selection and amplification. Currently, no microfabricated prototype platform is capable of carrying out a complicated process such as in vitro selection. Work proposed here is focused on development of a chip matrix prototype (validated by characterization of aptamer products) capable of integrated, iterative in vitro selection. Even if application of the in vitro selection process (SELEX) to that of a single chip microfluidic device remains distant at the conclusion of this project, the matrix approach will have 1) advanced the application of the in vitro selection process (SELEX) possibly making it more accessible for many applications and 2) yielded well characterized target specific aptamers.